Various documents using leader lines have been created. In design or production engineering sectors of the manufacturing industry, for example, for the purpose of explaining parts constituting products and explaining how to assemble parts, documents that illustrate parts and describe explanations about parts such as assembly drawings, part drawings, exploded drawings, and assembly instruction manuals are created. In such a document, in order to indicate a part corresponding to an explanation, a leader line is attached to the part.
There are various kinds of techniques that arrange such a leader line in an easy-to-see manner. For example, there is a technique that arranges leader lines extending from parts so that they do not cross each other. Conventional technologies are described in Japanese Laid-open Patent Publication No. 06-83881, Japanese Laid-open Patent Publication No. 02-264367, Japanese Laid-open Patent Publication No. 2002-324085, Japanese Laid-open Patent Publication No. 2002-324086, and Japanese Laid-open Patent Publication No. 2003-330970, for example.
Although the conventional technologies can arrange leader lines so that they do not cross each other, correspondences between leader lines and parts may be difficult to understand. The conventional technologies do not determine with which position of a part as a starting position a leader line is drawn. Given this situation, for example, leader lines are drawn with the gravity center position of a three-dimensional model of a part generated by computer aided design (CAD), the first apex position on data of the three-dimensional model, or the like as a starting position. In this case, in an assembly model including a plurality of parts, the starting position of a leader line of a part may be hidden behind other parts, and a correspondence between the leader line and the part is difficult to understand.